The jacket of an offshore drilling platform is the elongated tubular lattice that extends from a base to the deck of the platform, encloses the conductor pipes, and to which deck modules are fitted. The jacket is prefabricated onshore and loaded aboard a launch barge on its side by sliding it along skid rails onshore and then onto skid rails on the deck of the barge.
The launch barge is typically a flat-bottomed and flat-decked barge having a large clear deck space for receiving the jacket. The jacket is temporarily welded to the barge with bracing material and then transported to the installation site. The launch barge is fitted with a tilting mechanism by means of which the jacket can be caused to slide into the water. At the installation site, the bracing is cut and jacks are employed to slide the jacket along the skid rails until its center of gravity is properly located relative to the tilting mechanism, and the jacket is then slid off the tilting mechanism into the water.
Launch barges must be skillfully designed to accomodate the significant loads imposed by the weight of the jacket, the launch stresses, and the normal forces encountered while the barge is underway. In order to increase the capacity of the launch barge so that it can carry greater structural weight, permanent alterations have had to be made to the barge. Such alterations include the permanent addition of sponsons, deck strapping, and additional barge length. The addition and removal of such additions is labor intensive, time consuming, and quite expensive.
It is an object of the invention to provide a variable capacity barge by the quick and inexpensive connection and disconnection of one or more barge extensions.
It is another object of this invention to provide a hinged or articulated barge to transport and launch large structures and one which transmits the sheer forces across the hinge but not the bending moments that are created as a consequence of the transporting and launching of these structures.
It is a further object of this invention to gravity launch large buoyant structures from a barge taking into consideration the position of the structures' center of gravity with respect to the barge.
A further object of this invention is to provide a barge and a launching mechanism capable of withstanding the large forces that develop during the launching operation.